Sonar dome window damping and application procedure

ABSTRACT

A bow mounted steel sonar dome has a steel plating mounted on a rigid trusswork of circular rods and flat bars. Acoustically transparent damping tiles of graphite filled polymeric composite are mounted on the inside of the steel plating in a manner to prevent the entrapment of air between the plating and the damping tiles. Each damping tile has a plurality of tapered holes to allow any entrapped air between the steel and damping tile to collect in an adhesive slug that develops in the hole during manufacture.

United States Patent Phelps, Jr. et al.

1 1 Sept. 30, 1975 1 1 SONAR DOME WINDOW DAMPING AND APPLICATIONPROCEDURE [751 Inventors: Howard Neile Phelps, Jr., Coventry,

R.l.; Daniel Dinsmore, Jr., East Lyme, Conn.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

[22] Filed: Aug. 29. 1974 1211 Appl. No.: 501,511

52] U.S. Cl. 181/198; 181/175; 340/8 D Int. C1. A47B 81/06; G10K 11/00[58] Field 01Search..... 181/198, 175 33 G 33 GE, 181/33 R; 340/8 D [56]References Cited UNITED STATES PATENTS 2,884,084 4/1959 Sussman 1.181/175 3.038551 6/1962 McCoy et all i t 181/198 3,120,875 2/1964 Graner4. 181/198 3.136.380 6/1964 McCoy et al. 181/198 3,421,597 H1969 Blau eta1 181/33 R 3,647.022 3/1972 Meyer et a1 181/33 G FOREIGN PATENTS ORAPPLlCATlONS 611,318 10/1948 United Kingdom 340/8 D Primary E\aminerStephen .1. Tomsky Attorney, Agent, or FirmRiehard Si Sciascia;Arthur A. McGill; Prithvi C. Lall {57] ABSTRACT A bow mounted steelsonar dome has a steel plating mounted on a rigid trusswork of circularrods and flat bars. Acoustically transparent damping tiles of graphitefilled polymeric composite are mounted on the in side of the steelplating in a manner to prevent the entrapment of air between the platingand the damping tiles. Each damping tile has a plurality of taperedholes to allow any entrapped air between the steel and damping tile tocollect in an adhesive slug that develops in the hole duringmanufacture.

4 Claims, 5 Drawing Figures U.S. Patent Sept. 30,1975 Sheet 1 of53,908,790

FlG.l

US. Patent Sept. 30,1975 Sheet 2 of5 3,908,790

US Patent Sept. 30,1975 Sheet4 0f5 3,908,790

U.S. Patent Sept. 30,1975 Sheet 5 of5 3,908,790

SONAR DOME WINDOW DAMPING AND APPLICATION PROCEDURE STATEMENT OFGOVERNMENT INTEREST The invention described herein may be manufacturedand used by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefore.

BACKGROUND OF THE INVENTION The present invention generally relates tosonar systems and more particularly to a means for reducing sonar domedeterioration due to external coating and structural fatigue failures.

Since the introduction of steel bow-mounted sonar domes into the NavyFleet the above mentioned failures have frequently occurred. Thesefailures cause increased sonar self-noise levels, fouling of the domeexterior and water leakage in the domes. In fact, most domes of the typeinvolved are left uncoated on the outside due to the inability ofantifoulant coatings to remain on the steel; thus, the domes corrode andfoul. The seriousness of the dome problem was first recognized in 1962,shortly after the first two AN/SQS-26 ships started to use their sonars.In 1964 investigations found that the basic cause of the domes problemwas due to acoustic excitation of the dome by the sonar. This causedextremely large vibration levels within the domes.

Two types of vibratory motion to be considered when analyzing theresponse of domes to acoustic excitation are the forced motion, whichgenerates the desired transmitted signal. and the free or reverberantmotion, which generates scattered sound.

Measurements were conducted to confirm the theory of the reason behindthe dome failures. Acceleration levels were measured on the window areaof a four foot by four foot sonar dome section constructed the same as afull scale AN/SOS-26 sonar dome. The acceleration levels varied from 70to 470 peak gs at various points on the dome window when the domesection was acoustically excited by a nine element AN/SQS-26 sonararray. From the experiment, it was determined that the plateaccelerations are the sum of the reverberant field and forced fieldaccelerations. When the two fields are inphase the maximum total plateacceleration is approximately three times larger than the forced plateacceleration. However, when the reverberant and forced field are notinphase, the resultant acceleration at some points can be considerablyless than the forced field acceleration. The plate acceleration levelsin an undamped steel ribbed sonar dome such the AN/SOS-26 dome increasethe overall dome transmis sion loss by approximately 1 dB. Additionaltransmission losses result from nonspecular scattering of energy by thedome when excited by the reverberant velocity field on the dome window.These high window acceleration levels also cause paint coating failures.

SUMMARY OF THE INVENTION Accordingly it is a general purpose and objectof the present invention to provide an improved sonar dome window. It isa further object to reduce the total window acceleration by a reductionin the reverberant ac celerations caused by the trusswork. Anotherobject is to provide a window capable of being withstanding highersource levels prior to the onset of dome window cavitation. Otherobjects are the production of a dome window wherein, the flow inducedcomponent of self noise is considerably reduced. coating failures areprevented and fatigue failures due to acoustic excitation areeliminated.

The above objects are accomplished in accordance with the presentinvention by providing a sonar dome having rigid trusswork as its frame.A plurality of special composite damping tiles are affixed to theinterior of the dome in a manner to provide the above objects whilebeing transparent to transmitted radiation along a predetermined axis.In addition the construction is such that entrapped air problems areobviated by the use of an air free tile application.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view ofa typical sonardome adaptable for use with the present invention;

FIG. 2 is an interior view of the sonar dome of FIG. 1 prior toinstallation of the damping tiles;

FIG. 3 is a view of a typical damping tile used in the interior at thesonar dome of FIG. 1;

FIG. 4 shows the installation of the damping tile of FIG. 3; and

FIG. 5 shows the tile of FIG. 3 after installation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the figures andparticularly to FIG. I there is shown a sonar dome 10. The dome 10 shownis in AN/SQS-23 bow dome and is typical of a dome 10 that may beutilized in the present invention. The dome 10 has a base 12 and liftingring 14. The skin or steel plating 16 of the dome l0 SI'IIOWI'I isconstructed of A inch thickness HY- steel plating.

FIG. 2 shows a portion of the interior of the dome 10 with its rigidtrusswork 17. The trusswork 17 is comprised of a plurality of circularrods 18. Flat bars may be used in place of the rods 18, particularly inthe area of the interior skin 16. FIG. 3 shows a typical damping tile 22prior to its insertion in the system. The tile 22 is a graphite orcarbon black filled polymeric composite accoustically transparentdamping tile such as MIL- P-23653 Class 2 plastic damping tiles havingcavitation resistance. The tile 22 has a plurality of tapered holes 24whose use will be explained later.

The method of applying the tiles 22 to the rearward surface of theplating 16 is best shown with reference to FIG. 4. The entire interiorsurface of the plating I6 is sandblasted to obtain a surface roughnessof 1.5 to 2.5 mils. A film thickness of a maximum of .5 mils of a washprimer is then sprayed over the sand blasted area. Four coats of amoisture curing polyurethane with each coat having a thickness of about2.7 mils is then applied over the primer. From /2 to 6 hours must lapsebetween coats. At least 4 days must lapse after the final coat ofpolyurethane before the damping tile installation can begin. Eachdamping tile 22 having a dimensions of approximately 12 inches by 12inches by inch thick has 9 to 16 tapered holes drilled through it sothat the top of the hole has a diameter of about 1 /8 inch and thebottom of the hole has a diameter of about /8 inch. The purpose ofthetapered holes is to allow any entrapped air between the steel plating l6and damping tile 22 to collect in an adhesive slug that develops in thehole during the curing process. Each tile 22, to be inserted between thetrusswork l7 must be cut to fit each individual panel to be damped. Thetile should cover the metal surface to within /2 inch of the welds andnot extend over any welds.

The damping tiles 22 have an adhesive epoxy applied to them to bond thetiles 22 to the steel plating 16. Prior to application of the adhesive,the interior surface of dome and the tile 22 surface must be clean anddry. In applying the tiles 22 to the plating 16 a'lternate panels shouldbe clamped in checkerboard pattern. After the adhesive has cured onthese panels, the remaining panels should be damped. An even coat ofadhesive should be smoothly trowelled on both the steel plating 16surface and the tile 22 surface. All entrapped air in the adhesivelayers must be worked out. The coated tile 22 is then pressed firmlyagainst the center of the panel.

As shown in FIG. 4 a thin sheet of polyethylene 30 is next placed overthe tile 22. An inflatable installation bag 32, slightly larger insurface area than the tile 22 is placed over the tile 22 with thepolyethlene sheet 30 between the tile 22 and the inflatable installationbag 32. Next a steel plate 34 is placed over the installation bag 32.The plate 34 has an aperture 36 in the center to allow an air valve 38on the installation bag 32 to extend therethrough. A plurality of clamps40 that are adjustable in length are then inserted between the edge ofthe outer circular rods and the steel plate 34 thus clamping theassembly in place. The inflatable installation bag 32 is then inflatedto a pressure of approximately PSIG. The pressure is maintained on thetile for at least 12 hours permitting the adhesive to cure. After thecuring of the adhesive, the pressure is released and all of theinstallation equipment is removed.

Referring now to FIG. 5, there is shown at this time adhesive plug 42formed within a hole 26 of the damping tile 22. The adhesive plugs 42formed contain entrapped air that has flowed into the holes 26 of thetile 22. These plugs 42 are snapped out by means ofa screw driver orother sharp instrument providing an air free tile application. Theprocedure is then repeated for each panel 22 to be applied. The opening44 shows the appearance of hole 26 after removal of plug 42.

There has therefore been shown an improved sonar dome 10 having reducedsonar dome window vibrations, increased dome window cavitationthreshold, reduced fatigue failure and other improvements. The method ofmaking the device shows an air free method of applying tiles 22 under aconstant pressure to the inner surface of the skin 16 of dome 10.

It will be understood that various changes in the details, materials,steps and arrangement of parts, which have been made herein describedand illustrated in order to explain the nature of the invention, may bemade by those skilled in the art within the principal and scope of theinvention as expressed in the appended claims.

What is claimed is:

l. A sonar dome comprising:

a shell enclosure;

a rigid trusswork connected to the interior of said shell enclosure; and

a plurality of damping tiles affixed to the interior surface of saidshell with each tile having a plurality of apertures.

2. A sonar dome according to claim 1 with each said tile apertureshaving a wider diameter at the end away from said shell than at the endproximate said shell.

3. A sonar dome according to claim 2 wherein said tiles comprisegraphite filled polymeric composite.

4. A sonar dome according to claim 3 wherein said tiles comprise carbonblack material.

1. A sonar dome comprising: a shell enclosure; a rigid trussworkconnected to the interior of said shell enclosure; and a plurality ofdamping tiles affixed to the interior surface of said shell with eachtile having a plurality of apertures.
 2. A sonar dome according to claim1 with each said tile apertures having a wider diameter at the end awayfrom said shell than at the end proximate said shell.
 3. A sonar domeaccording to claim 2 wherein said tiles comprise graphite filledpolymeric composite.
 4. A sonar dome according to claim 3 wherein saidtiles comprise carbon black material.